Abstract. The comparative reactivity method (CRM) has been developed more than a decade to measure OH reactivity (i.e. OH loss frequency) in both laboratory and field studies. However, accurate OH reactivity quantification remains challenging under real ambient condition, especially for OH reactivity measurements in high-NO_X (e.g. > 10 ppbv) environments, as ambient NO enhance regeneration of OH radicals in the CRM reactor. To resolve this problem, we design a new improved CRM reactor (ICRM) and add NO into the system continuously, so that the HO₂ radical concentration is suppressed. We confirmed the appropriate level of NO by determining the maximum decrease in the pyrrole level caused by regenerated OH radicals from NO + HO₂. VOC-induced RO₂ radicals in the ICRM reactor were also found to react with NO, which lead to the re-generation of OH radicals thus the underestimation of OH reactivity. This effect was quantified by the calibration of representative VOC species at different NO levels, and the correction coefficients obtained were used to correct the measured OH reactivity. All these efforts resulted in reducing the uncertainty of the NO-artifact correction by at least an order of magnitude compared to the original CRM system. Additionally, these technological improvements also considerably reduced the systematic errors from pyrrole photolysis that exists in the original system. A new operation mode was proposed for ICRM, which is able to avoid the interference resulting from OH radicals produced by photolysis of residual humidity and save time for ambient measurement. The ICRM system was employed in a field campaign to measure OH reactivity and performed well with ambient NO levels ranged from 0 to 50 ppbv, which were typically observed in urban and suburban atmosphere.

中文翻译：

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改进的比较反应性方法（ICRM）：在高NO _X条件下在环境空气中测量OH反应性

摘要。在实验室和现场研究中，已经开发了比较反应性方法（CRM）来测量OH反应性（即OH损失频率）。但是，准确的OH反应性定量在实际环境条件下仍然具有挑战性，尤其是对于高NO _X（例如> 10 ppbv）环境中的OH反应性测量，因为环境NO会增强CRM反应器中OH自由基的再生。为了解决这个问题，我们设计了一种新型的改进型CRM反应器（ICRM），并向系统中连续添加NO，从而抑制了HO ₂自由基浓度。通过确定由NO + HO ₂再生的OH自由基引起的吡咯水平的最大降低，我们确定了合适的NO水平。VOC诱导的RO₂还发现ICRM反应器中的自由基与NO反应，这导致OH自由基的再生，因此低估了OH反应性。通过在不同NO浓度下对代表性VOC种类进行校准来量化此影响，并使用获得的校正系数来校正测得的OH反应性。所有这些努力导致与原始CRM系统相比，将NO伪影校正的不确定性降低了至少一个数量级。此外，这些技术改进还大大减少了原始系统中存在的吡咯光解带来的系统误差。提出了一种用于ICRM的新操作模式，该模式可以避免残留水分光解产生的OH自由基产生的干扰，并节省环境测量时间。